1a. Objectives (from AD-416)
In order to identify cold storage treatments that are efficacious against spotted wing drosophila (SWD) the project seeks to determine the most cold-tolerant stage of SWD, develop lethal exposure (LT) times necessary to produce 95, 99 and 99.9863% mortality of the most cold tolerant stage of SWD exposed to commercial cold storage conditions (0.5-2.2C and 90-95% RH), and determine rate of survival of SWD after SO2/CO2 fumigation and 21 day exposure to commercial cold storage conditions.
1b. Approach (from AD-416)
All SWD life-stages in artificial diet will be treated at 0.5C for 5, 10, 15, 20, and 25 days following the guidelines for optimal cold storage of table grapes. Probit analysis will be used to calculate LT values and identify the most cold tolerant stage, which will be used to estimate LT values for 2.2C, using the methods described above. Large-scale confirmatory tests using grapes infested with the most cold tolerant SWD stage and held in standard commercial shipping boxes will be done at 0.5 and 2.2C using the optimal treatment times derived above. Grapes infested with SWD will be treated with SO2/CO2 at the levels and times currently used for export to Australia/New Zealand and then held at 0.5 and 2.2C for 7, 14, 21 and 28 days. In all tests, treatment temperatures will be recorded with data loggers. Documents Trust with CAL Table Grape. Log 41966.
3. Progress Report
This research supports objective 3 (develop alternative physical treatments for dried fruits, nuts, and fresh fruits) of the in-house project, by providing data necessary to develop cold treatments for spotted winged drosophila (SWD). The goal of the project is to determine the length of time necessary to kill the most cold-tolerant life stage of the spotted wing drosophila (SWD) at commercial cold storage temperatures of 0.5-2.2C (33-36F). Preliminary studies were done using related Drosophila species to validate experimental methods while SPD cultures were established and increased. These preliminary studies showed that the pupal stage appeared to be the most cold tolerant, and suggests that pharate adults (adults not yet emerged) are capable of emerging during the cool down period. Future studies will determine the most cold tolerant stage of the SWD and the exposures necessary to kill the most tolerant stage at 0.5 and 2.2C, followed by confirmatory tests using grapes infested with the most cold tolerant stage.